U.S. patent application number 10/261614 was filed with the patent office on 2004-04-01 for impeller.
Invention is credited to Dickinson, Philip John, Makinson, Ian Douglas, Potharaju, Subbarao.
Application Number | 20040062648 10/261614 |
Document ID | / |
Family ID | 32030029 |
Filed Date | 2004-04-01 |
United States Patent
Application |
20040062648 |
Kind Code |
A1 |
Makinson, Ian Douglas ; et
al. |
April 1, 2004 |
Impeller
Abstract
An impeller includes a plastic disc, an annular array of vanes,
a rotation support and regions of permanently magnetisable
material. The plastic disc has an upper face and a lower face. The
vanes are spaced around the periphery of the disc and extend from
the upper face of the plastic disc. The rotation support is axially
located and aligned through the disc. The regions of permanently
magnetisable material encapsulated within said plastic disc for the
formation of an annular array of magnetic poles.
Inventors: |
Makinson, Ian Douglas;
(Auckland, NZ) ; Potharaju, Subbarao; (Auckland,
NZ) ; Dickinson, Philip John; (Auckland, NZ) |
Correspondence
Address: |
TREXLER, BUSHNELL, GIANGIORGI,
BLACKSTONE & MARR, LTD.
105 WEST ADAMS STREET
SUITE 3600
CHICAGO
IL
60603
US
|
Family ID: |
32030029 |
Appl. No.: |
10/261614 |
Filed: |
September 30, 2002 |
Current U.S.
Class: |
416/3 ; 416/170R;
416/241A |
Current CPC
Class: |
Y10T 29/49325 20150115;
B29L 2031/087 20130101; Y10T 29/49996 20150115; F04D 29/2222
20130101; Y10T 29/49316 20150115; F04D 25/0653 20130101; Y10T
29/49764 20150115; F04D 29/662 20130101; B29C 45/14065 20130101;
F04D 29/281 20130101; Y10T 29/4998 20150115; F04D 13/0606 20130101;
Y10T 29/49995 20150115 |
Class at
Publication: |
416/003 ;
416/170.00R; 416/241.00A |
International
Class: |
F04D 029/28 |
Claims
1. An impeller comprising: a plastic disc having an upper face and
a lower face, an annular array of vanes spaced around the periphery
of the disc and extending from said upper face, an axially located
and aligned rotation support passing through said disc, and regions
of permanently magnetisable material encapsulated within said
plastic disc for the formation of an annular array of magnetic
poles.
2. An impeller as claimed in claim 1 wherein said magnetisable
material comprises a ring of magnetisable material within said
disc, said ring and said disc each having a common axis of
symmetry.
3. An impeller as claimed in claim 2 wherein said rotation support
comprises a shaft passing through and extending from either side of
said disc, said shaft having a common axis of symmetry of said disc
and said ring.
4. An impeller as claimed in claim 3 wherein said disc includes a
hub portion spanning between an inner edge of said ring of
magnetisable material and an outer surface of said shaft, and in
said hub region, said upper face of said disc extends upward along
the outer surface of said shaft.
5. An impeller as claimed in any one of claims 1 to 4 further
including an annular plastic cap spanning amongst and connecting to
upper faces of said array of vanes, and having a central opening
there through.
6. An impeller as claimed in claim 4 including an annular plastic
cap spanning amongst and connecting with the tops of said annular
array of vanes, and having a central opening there through above
said hub portion of said disc, with an upper end of said shaft
protruding into said central opening.
7. An impeller as claimed in claim 6 wherein said vanes are
integrally moulded with said cap, extending from a lower surface of
said cap and having lower ends which contact and are secured with
said upper base of said disc.
8. A method of manufacturing an impeller comprising the steps of:
(a) forming an impeller having a plastic disc body and magnetisable
material distributed and encapsulated within said body; (b) testing
the imbalance of said impeller; (c) removing plastic material from
said impeller to compensate for said tested imbalance; (d)
magnetising said magnetisable material to have an annular array of
alternating poles.
9. A method as claimed in claim 8 wherein said step of forming said
impeller comprises the steps of: (a) (i) locating a ring of
magnetisable material in an injection mould, including centrally
locating said ring by engaging an outer surface thereof at spaced
locations around said surface; (a) (ii) locating a shaft centrally
within said mould, passing through said ring such that said shaft
and said ring have a common axis of rotational symmetry; and (a)
(iii) injecting plastic into said mould to encapsulate said ring of
magnetisable material and span between said ring and said shaft;
(a) (iv) extracting said impeller from said mould.
10. A method as claimed in claim 9 wherein forming said impeller
includes the additional steps of: (a) (v) forming an annular
plastic cap having a lower face and an array of impeller vanes
distributed around and extending from said lower face; and (a) (vi)
securing said cap to an upper face of said disc by connecting the
free ends of said vanes to said upper face.
11. A method as claimed in claim 8 wherein said step of testing for
imbalance includes testing for static imbalance and dynamic
imbalance, and said step of compensating for imbalance includes
removing plastic material at at least two axially separated
locations on the periphery of said disc.
12. A method as claimed in claim 10 wherein said step of testing
for imbalance includes testing for static imbalance and dynamic
imbalance, and said step of compensating for imbalance includes
removing plastic material at at least one location on said disc and
at least one location on said cap.
13. An impeller manufactured according to the method of any one of
claims 8 to 12.
Description
BACKGROUND TO THE INVENTION
[0001] The present invention relates to fan impellers and methods
of manufacturing and balancing impellers. In particular the present
invention relates to improvements in the manufacture and balancing
of impellers wherein the rotor body and impeller are integrally
formed.
[0002] 1. Summary of the Prior Art
[0003] In traditional blower assemblies, an impeller is driven by a
motor coupled to it. A disadvantage of these traditional blowers is
the complexity due to the number of parts which need to be
assembled and thus may contribute significantly to cost.
[0004] The assembly of rotors from a number of parts may also
require the individual parts to be accurately formed and assembled,
in order to reduce imbalance of the completed rotor product.
[0005] 2. Summary of the Invention
[0006] It is an object of the present invention to provide an
impeller for a blower, which will at least go some way towards
improving on the above or which will at least provide the industry
with a useful choice.
[0007] Accordingly in a first aspect the present invention consists
in an impeller including:
[0008] a plastic disc having an upper face and a lower face,
[0009] an annular array of vanes spaced around the periphery of the
disc and extending from said upper face,
[0010] an axially located and aligned rotation support passing
through said disc, and
[0011] regions of permanently magnetisable material encapsulated
within said plastic disc for the formation of an annular array of
magnetic poles.
[0012] Preferably said magnetisable material comprises a ring of
magnetisable material within said disc, said ring and said disc
each having a common axis of symmetry.
[0013] Preferably said rotation support comprises a shaft passing
through and extending from either side of said disc, said shaft
having a common axis of symmetry of said disc and said ring.
[0014] Preferably said disc includes a hub portion spanning between
an inner edge of said ring of magnetisable material and an outer
surface of said shaft, and in said hub region, said upper face of
said disc extends upward along the outer surface of said shaft.
[0015] Preferably said impeller may further include an annular
plastic cap spanning amongst and connecting to upper faces of said
array of vanes, and having a central opening there through.
[0016] Preferably said impeller may include an annular plastic cap
spanning amongst and connecting with the tops of said annular array
of vanes, and having a central opening there through above said hub
portion of said disc, with an upper end of said shaft protruding
into said central opening.
[0017] Preferably said vanes are integrally moulded with said cap,
extending from a lower surface of said cap and having lower ends
which contact and are secured with said upper base of said
disc.
[0018] In a second aspect the present invention consists in a
method of manufacturing an impeller comprising the steps of:
[0019] (a) forming an impeller having a plastic disc body and
magnetisable material distributed and encapsulated within said
body,
[0020] (b) testing the imbalance of said impeller;
[0021] (c) removing plastic material from said impeller to
compensate for said tested imbalance;
[0022] (d) magnetising said magnetisable material to have an
annular array of alternating poles.
[0023] Preferably said step of forming said impeller comprises the
steps of:
[0024] (a) (i) locating a ring of magnetisable material in an
injection mould, including centrally locating said ring by engaging
an outer surface thereof at spaced locations around said
surface;
[0025] (a) (ii) locating a shaft centrally within said mould,
passing through said ring, such that said shaft and said ring have
a common axis of rotational symmetry; and
[0026] (a) (iii) injecting plastic into said mould to encapsulate
said ring of magnetisable material and span between said ring and
said shaft;
[0027] (a) (iv) extracting said impeller from said mould.
[0028] Preferably said impeller includes the additional steps
of:
[0029] (a) (v) forming an annular plastic cap having a lower face
and an array of impeller vanes distributed around and extending
from said lower face; and
[0030] (a) (vi) securing said cap to an upper face of said disc by
connecting the free ends of said vanes to said upper face.
[0031] Preferably said step of testing for imbalance includes
testing for static imbalance and dynamic imbalance, and said step
of compensating for imbalance includes removing plastic material at
at least two axially separated locations on the periphery of said
disc.
[0032] Preferably said step of testing for imbalance includes
testing for imbalance includes testing for static imbalance and
dynamic imbalance, and said step of compensating for imbalance
includes removing plastic material at at least one location on said
disc and at least one location on said cap.
[0033] To those skilled in the art to which the invention relates,
many changes in construction and widely differing embodiments and
applications of the invention will suggest themselves without
departing from the scope of the invention as defined in the
appended claims. The disclosures and the descriptions herein are
purely illustrative and are not intended to be in any sense
limiting.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a perspective view of an encapsulated rotor
according to a first embodiment of the present invention.
[0035] FIG. 2 is a perspective view of the rotor pictured in FIG. 1
showing the underside.
[0036] FIG. 3 is a mid transverse cross section view of the
impeller shown in FIG. 1.
[0037] FIG. 4 is an exploded assembly view of an encapsulated rotor
according to a second preferred embodiment of the present
invention.
[0038] FIG. 5 is an exploded assembly view of the rotor shown in
FIG. 4 shown from a different angle.
[0039] FIG. 6 is a perspective view of an encapsulated rotor
according to the second embodiment of the present invention.
[0040] FIG. 7 is a cross section view of the mould apparatus used
to overmould an encapsulated rotor according to the present
invention.
[0041] FIG. 8 is a plan view of the mould apparatus pictured in
FIG. 7.
[0042] FIG. 9 is a perspective view of the balance measuring
apparatus.
[0043] FIG. 10 is a end elevation view of an encapsulated rotor
according to the second preferred embodiment of the present
invention showing the location of the material to be removed for
balancing.
[0044] FIG. 11 is a plan view showing the milling paths pictured in
FIG. 10.
[0045] FIG. 12 is a cross-section view of an impeller according to
the first preferred embodiment of the present invention installed
in a blower housing.
DETAILED DESCRIPTION
[0046] With reference to FIGS. 1 to 3 a first preferred embodiment
of the present invention will be described. The present invention
discloses an impeller having a plurality of impeller blades 1
moulded over the permanent magnets of an electric motor rotor. A
shaft 2 is also integrally moulded into the rotor assembly during
the manufacturing process. The rotor/impeller of the present
invention is suitable for use in a pressurised gases supply device
such as a CPAP blower. It is also envisaged that the rotor/impeller
according to the present invention may provide advantages for any
blower/fan application.
[0047] FIG. 12 shows an impeller according to a first preferred
embodiment of the present invention installed in a blower housing.
Air enters through inlet port 31 where it is blown through the
outlet volute 32. Arrows 33 show the position where a commutated
stator goes in order to provide a torque to the rotor.
[0048] The resulting assembly is a compact, one piece combined
rotor and impeller. The integral forming of the rotor and impeller
allow for significant simplification of traditional designs and may
lead to a more cost effective product.
[0049] The rotor 4 is generally disc shaped. A shaft 2 extends
through the centre of the disc, protruding on both sides in a
direction that is normal to the general plane of the disc, so that
it is coaxial with the rotor 4. On one face of the disc a plurality
of impeller vanes 1 is arranged in an annular array. The impeller
vanes have a curved profile shaped in accordance with the
performance requirements of the blower. The impeller is moulded
over a magnetisable element 3. The element 3 subsequently
magnetised to become the permanent magnetic poles of the rotor. In
use the poles interact with a commutated stator to provide a torque
to the rotor/impeller assembly.
[0050] Between the inner face of the magnetisable element 3 and the
outer surface of to the shaft 2 is a hub portion 14. The inner
portion of the hub 14 extends upward along the outer surface of the
shaft 2 forming a shoulder portion 17. The upperside of the hub 14
is a thin shell. The underside of the hub portion 14 is a plurality
of annularly spaced ribs 15. Shaft 2 may include a groove 5 adapted
to receive a circlip for the purpose of securing the rotor.
[0051] Performance of the encapsulated rotor will be detrimentally
effected by any imbalance arising from asymmetry of the components
about its axis of rotation. In traditional designs where the
impeller is not integrally formed to include the permanent magnets
of the rotor, the impeller will be comparatively lightweight.
Consequently there is less potential for significant imbalance when
the impeller is comparatively lighter. In an encapsulated rotor
such as that described in the present invention the integral
forming of the permanent magnets with the impeller blades
dramatically increases the potential for significant rotational
imbalance. Consequently it is advantageous for rotors formed
according to the present invention to be as close as possible to
being balanced once the overmoulding process has been completed. In
order to achieve this the present invention precisely locates and
maintains the position of the shaft and magnet(s) in the
overmoulding process.
[0052] In this first preferred embodiment of the present invention
the impeller is moulded over a one piece magnetisable ring 3. A
small portion of the outer surface of magnetisable ring 3 is
visible through aperture 7 in FIG. 2. The ring 3 is subsequently
magnetised to have four poles.
[0053] With reference to FIG. 7, the ring 3 is inserted into the
mould cavity against a plurality of upwardly projecting support
rods 12. The rods support the ring 3 and hold it slightly off the
bottom surface of the mould cavity thus allowing the injected
molten polymer to flow around the ring encapsulating it from all
sides. It is advantageous that the wall thickness of the
encapsulating polymer on the bottom surface of the magnetisable
ring 3 is as thin as practicable in order that the air gap between
the ring 3 and the coils of the stator is small. The portion on the
bottom surface of the ring 3 which is in contact with the plurality
of supporting rods 12 will not be covered in plastic. This results
in detents 6 in the finished product. A reference mark 21 is also
produced in the finished product via a similar process that
produces the detents 6. The reference mark is used later in the
balancing process. It is a requirement that the reference mark 21
is distinguishable (by an optical sensor) from the detents 6. In
the preferred embodiment of the present invention the reference
mark 21 is distinguished from detents 6 by its shape and its
position. Reference mark 21 is a slot and is positioned closer to
the outer edge of the rotor body 4 than detents 6.
[0054] In order to align the magnet ring 3 coaxially with the mould
cavity a number of alignment pins 13 are provided which extend into
the mould cavity around the periphery and substantially
perpendicular to the rods 12 as shown in FIG. 8. Alignment pins 13
are extendable and retractable in order to facilitate alignment of
the magnetisable ring 3 and the extraction of the completed rotor
product. In the preferred embodiment of the present invention there
are three alignment pins 13 arranged in the horizontal plane, 120
degrees apart. The alignment pins contact the outer surface of ring
3, in order to provide coaxial alignment between the mould cavity
and rig. The alignment pins 13 also allow molten plastic to flow
around them encapsulating the rotor. In a similar manner to detents
6, the alignment rods form outer detents 7 in the finished rotor
product.
[0055] Provided in the lower platen of the mould, is a locating
recess 8 for shaft 2. The shaft recess 8 is shaped and positioned
such that it may receive and accurately locate the shaft 2 to be
coaxial with the central axis of the mould cavity. Injection port 9
is conical and provides an opening into the mould cavity for the
injection of molten plastic. The injection port cavity also forms a
sprue on the finished product.
[0056] It is preferable to include a key for ensuring that rotation
between the shaft 2 and the finished moulded impeller does not
occur. To this end the shaft 2 is provided with at least one
protrusion to engage with the moulding. In the preferred embodiment
of the present invention a splined section 10 is provided on the
shaft for this purpose.
[0057] During the manufacturing process an annular magnetisable
ring 3 is inserted into the mould cavity 11 so that its bottom
surface rests on and is supported by the plurality of rods 12. The
alignment pins 13 are then extended so that they bear upon the
outer surface of ring 3 aligning the ring to be coaxial with the
central axis of the mould cavity. A shaft 2 is placed into shaft
recess 8 which is also aligned with the central axis of the mould
cavity. After the mould halves are closed and pressed together
molten plastic is injected through injector port 9 until the mould
cavity is filled. A sprue is formed in he injector cavity 9 and is
later removed when the finished product has cooled.
[0058] In order to remove the finished impeller from the mould it
is necessary to retract alignment pins 13 so that their inner ends
are removed from the detents 7 of the finished product which allows
the finished product to be displaced axially and removed from the
mould. The support rods 12 are able to extend and retract so that
they can be used to eject the finished product from the mould.
[0059] With reference to FIGS. 4 to 6 a second preferred embodiment
of the present invention will be described. It has been found that
a number of advantages can be obtained by including a cap 20
enclosing the upper edges of the impeller vanes. The cap reduces
the amount of air spilling over top of the vanes and improves the
impeller's performance.
[0060] In the second preferred embodiment of the present invention
the impeller assembly incorporates a cap enclosing the vanes of the
impeller. The additional cap on the impeller blades makes it
considerably more difficult to overmould an accurate vane structure
in a single operation. FIG. 5 shows an exploded assembly view
showing the impeller structure being formed from shaft 2,
magnetisable ring 3, rotor body 4 and impeller/end cap ring 20.
[0061] The main rotor body 4 is moulded over a one piece
magnetisable ring which is magnetised to have four poles. The rotor
body has a protruding sleeve portion 17 extending axially from the
middle of the disc shaped rotor body. The rotor body has on its
upper surface a plurality of shallow grooves 19 spaced around its
circumference in order to provide a locating feature for the
impeller vanes 1.
[0062] The grooves 19 are shaped and positioned so that they may
locate the impeller vanes 1 during assembly of the impeller. The
upper surface of the vanes 1 may also include a plurality of small
ridges (not shown) to aid in ultrasonic welding between the vanes
and the grooves. In the second preferred embodiment of the present
invention the performance of the impeller is improved by tapering
the vanes so that the cross section reduces toward the outside of
the rotor body. This feature helps to maintain a more constant
pressure and reduces flutter.
[0063] The rotor body is manufactured in the manner described above
except for manufacture of the one piece impeller of the first
embodiment. But the rotor body 4 does not include vanes. In an
analogous manner to the first embodiment of the present invention a
reference mark 21 is provided on the lower surface of the rotor
body 4. While it is possible to locate a reference mark on the top
surface of the rotor in the first embodiment of the present
invention, the impeller cap 20 of the second preferred embodiment
would obscure such a reference mark from the optical sensor.
Accordingly in the second preferred embodiment of the present
invention the reference mark 21 is located on the underside of the
rotor body 4. The reference mark is distinguishable from the
detents 6 due to its shape and position closer to the outer edge of
the rotor body 4.
[0064] It is envisaged that a capped rotor according to the second
embodiment of the present invention may be manufactured by adding
an end cap to an encapsulated rotor substantially as described in
the first embodiment of the present invention. In the most
preferred second embodiment of the present invention the impeller
vanes 1 are integrally formed with the cap and subsequently welded
to the rotor. The method described in the second embodiment of the
present invention is most preferred because it provides some
advantages during manufacture. Such advantages include:
[0065] Mould for rotor body is simpler.
[0066] During ultrasonic welding it is preferable that the abutting
surfaces to be welded are in the same plane.
[0067] Referring to FIGS. 4 to 8, dig manufacture an annular
magnetisable ring 3 is inserted into the mould cavity 11 so that
its bottom surface rests on and is supported by a plurality of rods
12. At least three alignment pins 13 are then inserted through the
mould cavity so that they bear upon the outer surface of ring 3
aligning the ring to be coaxial with the central axis of the mould
cavity. A shaft 2 is placed into shaft recess 8 which is also
aligned with the central axis of the mould cavity. After the mould
halves are closed and pressed together molten plastic is injected
through injector port 9 until the mould cavity is filled. A sprue
is formed in the injector cavity 9 which is later removed when the
body of the rotor has cooled A separate injection moulded part 20
is manufactured which includes the impeller cap and impeller
vanes.
[0068] In contrast to the first preferred embodiment of the present
invention this second embodiment requires further assembly to
complete the production of the impeller. The impeller cap 20 is
located in the correct position by aligning the impeller vanes 16
with the locating grooves 19 of the rotor body. A welding process
such as ultrasonic or vibration welding is then used to bond the
two parts together and finish the impeller product.
[0069] The benefits obtained from this improved impeller design
are:
[0070] The same flow pressure can be achieved with a reduced
rotational speed or produce a higher pressure for any given
rotational speed.
[0071] Traditional impeller designs may experience a significant
pressure drop at higher flow rates. The improved impeller design is
able to produce a more constant pressure throughout a range of flow
rates.
[0072] The improved impeller design may significantly reduce the
level of noise produced by the impeller when operating.
[0073] The impeller cap provides a second planar surface spaced
apart from the main rotor body. Material may be removed from two
planes with maximum axial separation axially which is advantageous
for balancing the rotor.
[0074] Rotors according to the above embodiments are manufactured
in a fashion that leads to accurate tolerancing and minimised
imbalance. However in order to improve the dynamic balance of
rotors according to the first or second preferred embodiments of
the present invention it may be advantageous to perform a dynamic
balancing. In order to do this a dynamic balancing apparatus
measures the imbalance in two planes and removes appropriate
amounts of plastic material from the circumference of the rotor.
The removal of material may be effected by a plurality of milling
tools, guided by measurements of the imbalance of the rotor. The
angular position and the size of each balancing notch formed by the
removal of material from the circumference of the rotor counteracts
the initial imbalance of the rotor.
[0075] The wall thickness of the material encapsulating the
magnetisable disc 3 is increased around the circumference 34 in
order to provide sufficient material which can be removed during
the balancing process. Similarly the top surface of the impeller
cap 20 is provided with a raised annular ring 16 of plastic
material which can be later removed for the purposes of balancing
the rotor.
[0076] In order for such dynamic balancing to be successful,
measurements of the initial imbalance are made from a reference
point. The amount of material to be removed in order to balance the
rotor is then calculated relative to the same reference point. In
removal of material through the milling process position is
determined relative to the same reference point for the purpose of
accurately removing the material as calculated.
[0077] In the present invention each impeller includes a reference
mark 21, in order to facilitate dynamic balancing of the rotor.
FIG. 9 shows a dynamic balancing device. Rotor 22 is rotatably
mounted in a holder 23. Air is supplied through conduits 24 and
directed onto the impeller vanes in order to spin the rotor. The
holder 23 is mounted on a plate 25. The holder includes a plurality
of sensors for determining the imbalance of the spinning rotor. In
order to reduce interference from environmental vibrations the
balancing apparatus is mounted on a solid suspension base which is
in turn mounted on vibration isolation mounts 26. An optical sensor
27 is provided in order to sense the reference mark on the rotor as
it rotates. A control device 28 receives information from the
cradle sensors and the optical sensor.
[0078] The control device is programmed to process the signals of
the cradle sensors and optical sensor, and determine an imbalance
of the rotor relative to the reference mark. The control device is
programmed to calculate appropriate material removal that will
compensate for the imbalance.
[0079] A milling station 18 includes a work piece holder 30 for
holding an impeller by its shaft. The work piece holder is driven
for precisely controlled angular and translational positioning.
[0080] With reference to FIGS. 10 and 11 a cutting tool 29 is spun
by the milling machine while the rotor/impeller is moved so that
the cutting tool may mill appropriate notches for balancing the
rotor as calculated by the balancing machine. The control device
calculates the angle, depth and length of the arc to remove the
correct mass of material at the correct angular position. In order
to orientate the milling machine the same reference mark 21 is
orientated to a known position relative to the milling machine.
[0081] The rotor is magnetised after the balancing process so that
the magnetic field does not interfere with the imbalance
measurement. The magnetising process consists of loading the rotor
onto a magnetising fixture. The fixture consists of a series of
coils wound around a soft magnetic material arranged to produce the
appropriate flux pattern to magnetise the ring 3. There is one coil
in the magnetising head corresponding to each magnetic pole on the
magnetisable ring 3 in the rotor. After the rotor has been loaded
onto the magnetising fixture, a bank of capacitors is discharged
through the coils in the fixture. This produces an extremely high
current pulse of approximately 20,000 amps for 10 microseconds. The
magnetic field that is produced is sufficient to permanently
magnetise the ring 3.
* * * * *